A ribonucleoprotein (RNP) catalyst capable of RNA aminoacylation will be assembled. This RNP will be based on a truncated form of alanyl-tRNA synthetase which synthesizes aminoacyl-AMP, but lacks an RNA recognition domain. Hence, in vitro selection methods will be employed to obtain a suitable RNA aptamer that will re-establish the ability of the catalyst to bind an RNA substrate. The aminoacylation efficiency for the resultant RNP will be investigated and the RNA-protein interfaces present within the complex will be characterized using biochemical techniques. It has been proposed that ribonucleoproteins were common catalysts during the period of evolution bridging RNA and protein- dominated worlds, and it is likely that the synthetases appeared very early in this transition because of their important role in protein synthesis. Thus, the assembly of an aminoacylating RNP would provide evidence for possible evolutionary precursors to the synthetases that contained RNA components.